Scintillation materials are used in the detection and measurement of radiation. Scintillators are composed of substances which are capable of absorbing energy given off by the fission fragments emitted by radioactive elements. The absorbed energy excites fluorescent materials contained in the scintillator, so that the fluorescent materials give off light. Such scintillators are useful in many different applications, e.g., the detection of radioactive mineral deposits, and the detection and measurement of radioactive contamination.
Plastics are often used as such scintillation materials. The plastic materials that have found the widest application consist of those manufactured from thermosetting plastics. These thermosetting plastics include polystyrene, polyvinyl toluene, and various acrylic polymers. The acrylic polymers are primarily employed for their cost effectiveness in fabrication of large volume scintillators.
The generation of light from these plastics is accomplished through the addition of small amounts of many different combinations of organic molecules known to have fluorescent properties of high efficiency. These molecules include p-terphenyl and naphthalene.
Hyman, Jr. U.S. Pat. No. 3,886,082, issued May 27, 1975, discloses an example of one such plastic scintillator material. The scintillator disclosed in the Hyman patent employs acrylic polymers and copolymers as the host plastic and bis-(o-methyl styryl)benzene, perylene, tetraphenylbutadiene, diphenylanthracene, bis(phenyloxazolyl benzene), and dimethyl bis(phenyloxazolyl benzene) as the fluorescent additive.
Siegrist et al., U.S. Pat. No. 4,180,479, issued Dec. 25, 1979, discloses the use of various stilbene derivatives as fluorescent agents in scintillators.
U.S. Pat. No. 4,495,084 to Shimizu et al discloses plastic scintillators in which a scintillating substance is incorporated into a matrix resin which comprises a copolymer of a styrene type compound and various unsaturated copolymers including unsaturated esters.
U.S. Pat. No. 3,010,908 to Broderick et al also discloses fluorescent plastic scintillators which are based on styrene type polymers.
U.S. Pat. No. 3,068,178 is concerned with liquid scintillators for fluorescence. In column 5, plastic scintillators are discussed, including those based on polystyrene and polyvinyltoluene.
In U.S. Pat. No. 3,600,445 to Wirth et al there are disclosed organic scintillators such as para-terphenyl, 2,5-diphenyloxazol (PPO), and 2,5-bis-[5'-tertiarybutyl-benzoxazolyl-(2')]-thiophen.
In U.S. Pat. No. 2,745,967 to Ludeman, radiation conductors are disclosed which include polystyrene and polymerized methylmethacrylate.
In a publication by Birks in "Scintillation Counters", McGraw Hill Book Company, New York, NY, 1953, pages 102-105, there is a discussion regarding the scintillation properties of anthracene and stilbene when dissolved in polystyrene, Lucite, and Parplex, which are all transparent plastics. Organic solutions of phosphors are also disclosed.
In a publication in The Journal of Chemical Physics, Vol. 67, No. 11, Dec. 1, 1977 by Mitchell et al, there are disclosed high pressure studies of fluorenone emission in plastic media. In this article, fluorenone flourescence was studied, and in the experimental section, the study was carried out by pressing pellets of polymethylpentene between hot plates to make films approximately 0.2 millimeters thick. The films were then soaked in a hexane solution of fluorenone and dried and washed with methanol to provide samples of the fluorenone. A similar study was carried out with polyisobutylene. The luminescence was then studied using these structures. However, this is not use of the polymethylpentene as the host plastic in a plastic scintillator.
The prior art scintillators have the major disadvantage that none of the host polymers have been found suitable for use at temperatures up to and above 200.degree. C. For example, the maximum temperature of non-cross linked polyvinyl toluene is 75.degree. C.; and that of cross-linked polyvinyltoluene is 100.degree. C. The prior art polymers with the highest temperature resistance are the acrylic co-polymers, with a maximum temperature of 150.degree. C.